1. Field of the Invention
This invention relates to a novel microorganism and a method for the selection thereof. More particularly, it relates to a strain Lactobacillus bulgaricus OLL 1074 which is sensitive to a lower temperature in the meaning that it shows a weak tendency towards lactic acid formation at a lower temperature range, and the method for the selection thereof.
The invention also relates to a novel fermented milk or lactic beverage, the method for the preparation thereof and, more particularly, to such beverage obtained by employing the strain Lactobacillus bulgaricus OLL 1074 which is sensitive at a lower temperature in the sense that it shows a weak tendency towards lactic acid formation at a lower temperature range, and the method for the preparation thereof.
2. Description of the Prior Art
The yoghurt is a typical fermented milk product known from old and produced by using the strain Lactobacillus bulgaricus and the strain Streptococcus thermophilus as the main starters. That is, the starting milk material known as yoghurt mix is inoculated with the aforementioned lactic acid bacteria starters and fermented at 40.degree. to 46.degree. C. for several hours. As the fermented product has reached a proper acidity, it is stored in cold state for stopping fermentation and marketed in this state.
Although fermentation of the yoghurt for forming lactic acid is considerably suppressed by such cold preservation, it is not suppressed completely. Even during cold preservation, lactic acid is produced gradually to increase the sour taste so that it is very difficult to maintain the fresh sour taste proper to the newly manufactured yoghurt during the subsequent preservation and distribution periods.
While it is known to sterilize the yoghurt immediately after manufacture thereof to enhance its keeping quality, the yoghurt obtained in this way does not containg live bacteria so that the merit proper to the yoghurt that it contains a live microorganism is lost. As other methods for preventing the increase in the acidity of the yoghurt during preservation thereof, it is also known to heat the yoghurt for a certain period of time and at a temperature higher than the high side growth cessation limit temperature of the lactic acid bacteria and lower than the temperature for complete extinction thereof (Japanese Laying-open Patent Publication No. 6745-1975) or to make use as the starter of a variant M-13 incapable of fermenting lactose for lactic acid formation and artificially transformed from the strain Lactobacillus jugurti (Japanese Laying-open Patent Publication No. 38187-1979). However, with the method described in the Laying-open Patent Publication No. 6745-1975, the process is complicated since there is involved a step of preserving a batch of material at a lower temperature, heating and again cooling it, thus entailing a consumption of an excess heat energy, while it is also difficult to control the temperature and the number of live bacteria. With the method described in the Laying-open Patent Publication No. 38187-1979, since the fermentable sugar of the variant Lactobacillus jugurti need be added to the culture medium, it is necessary to adjust the suger to a target acidity by a laborious operation. In addition, it is not possible with the method to prepare the plain type yoghurt for which an increasing demand is raised among general consumers.